Range Hood Venting


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Old 06-27-12, 12:47 PM
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Range Hood Venting

I would like to install a microwave above the range that vents to the outside, but it looks challenging. Behind the range is the garage. Beneath the range is the basement. Above the range is a second floor bedroom. There are only two routes from the range to the outside. This is a townhouse with units on both sides.

1. Five or 6 ft down the wall behind the range to the basement and about 35 ft to the back of the house. The joist bay is full of water pipes, sewer pipes and vacuum pipes for a built-in vacuum system.

2. Five ft up the wall behind the range, about 10 ft along the garage ceiling and the bedroom floor, about 10 more ft through an attic cold space and down through the roof eave overhang. I assume there is insulation in the bedroom floor/garage ceiling and insulation in the attic cold space. The garage wall and ceiling are finished with drywall.

I think neither option is very good, with #1 out of the question and #2 might be workable although I wonder about the length of run...some 25 ft.

I plan to cut an access through the garage ceiling to the attic space to verify the insulation because I have ice damming problems in the winter over this attic space.

Do you have any suggestions or comments about this venting challenge?
 
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Old 06-27-12, 12:55 PM
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IMO, best thing to do would be to check the wall behind the proposed range hood with a studfinder to determine where the studs are in relation to your range hood. Then open up the drywall on the garage side in the appropriate location, and insert your 3 1/4 x 10" duct into the stud cavity, running it straight up through the top plate and roof to a roof cap flashing.

Or are you saying you have a finished bedroom above part of your garage? If so, once you reach the ceiling (bedroom floor), you could transition to an 8" round flexible insulated duct, run it down the floor joists to the exterior wall, where it could then be vented through the exterior wall and out the roof above the soffit. Depending on the length of the run, a booster fan might be needed.

Alternatively, the 3 1/4 x 10" duct could stay on the interior side of the garage wall (putting the duct in the wall would make a cold spot since you would need to remove insulation in that exterior garage wall), and go up through the back of the wall cabinet and into the ceiling, where it would transition to an 8" duct and run parallel to the floor joists until it reaches an exterior wall. This would obviously only work if you have a soffit above the cabinets so that the duct could be hidden on its way up to the floor joists.
 
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Old 06-27-12, 01:51 PM
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This is purely an opinion as I don't want to keep you from venting to the outside. I have never used an outside vent on a microwave. Maybe I don't burn things that need venting That long a run will be formidable to say the least!! Why not just revent through the onboard filters?
 
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Old 06-30-12, 04:48 PM
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Venting to the outside is not because I burned something, but to exhaust moisture and cooking oders. It seems quite common to simply recirculate the moisture and oders back into the kitchen through grease filters and carbon filters.

So, if it is ok to recirculate into the kitchen, why wouldn't it be ok to exhaust into the garage through a similar filter system?
 
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Old 06-30-12, 05:03 PM
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I don't have a problem with venting to the outside. I had a client who insisted on a 800cfm roof mounted range hood vent . She didn't like fish smell, but loved to eat fish. That thing would suck a cat off the counter if it passed under it !!. She realized my initial comment on the system turned out to be true. Run an 800 cfm vent for more than 10 minutes and you have evacuated your entire house of heat or air conditioning. But no fish smell!!
Venting to a garage would violate code, anyway as the two must not have common air.
I question total removal of any moisture with the duct run you are being faced with, but if it is done right, maybe it will work.
 
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Old 07-01-12, 06:08 AM
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I haven't thought about cfm yet, but here is another reason to vent to the outside. Our current microwave recirculates back into the kitchen, and every time we use the self cleaning oven all the smoke alarms will eventually go off and we have to open windows and doors to clear the area while the dog goes crazy trying to get away from the squeel.
 
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Old 07-01-12, 09:30 AM
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Yeah, that noise can be obnoxious, as well as the smell. You may need to put a booster fan in line at some point, actuated by the microwave fan switch in order to increase the cfm enough to evacuate it all. Just fuel for the fire.
 
 

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